Liquid membranes for quantification and speciation of trace metals in natural waters

PVDF-HFP-based polymer inclusion membrane functionalized with D2EHPA for the selective extraction of bismuth(III) from sulfate media

This study is the first application of a PVDF-HFP-based polymer inclusion membrane incorporating the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and di(2-ethylhexyl)phosphoric acid (D2EHPA) as the base polymer and extractant for the extraction of bismuth(III), respectively. It is demonstrated that the PIM comprised of 60 wt% PVDF-HFP and 40 wt% D2EHPA is the most effective in the extraction of bismuth(III) from feed solution containing 20 mg L-1 bismuth(III) and 0.2 mol L-1 sulfate adjusted to pH 1.4. The extracted bismuth(III) ions are back-extracted quantitatively to the receiving solution containing 1 mol L-1 sulfuric acid. The stoichiometry experiments reveal that the Bi: D2EHPA ratio in the bismuth(III) extracted complex is 1:6, and D2EHPA is dimer. Moreover, it is shown that the studied PIM has high selectivity in the extraction of bismuth(III) over other interfering ions such as Mo(VI), Cr(III), Al(III), Fe(III), Ni(II), Zn(II), Cd(II), Co(II), Cu(II), and Mn(II). The interference of Fe(III) is also eliminated by masking with fluoride, leading finally to a nearly pure extraction of bismuth(III).

Recovery of copper and silver from industrial e-waste leached solutions using sustainable liquid membrane technology: a review

Waste electrical and electronic equipment or e-waste has recently emerged as a significant global concern. This waste contains various valuable metals, and via recycling, it could become a sustainable resource of metals (viz. copper, silver, gold, and others) while reducing reliance on virgin mining. Copper and silver with their superior electrical and thermal conductivity have been reviewed due to their high demand. Recovering these metals will be beneficial to attain the current needs. Liquid membrane technology has appeared as a viable option for treating e-waste from various industries as a simultaneous extraction and stripping process. It also includes extensive research on biotechnology, chemical and pharmaceutical, environmental engineering, pulp and paper, textile, food processing, and wastewater treatment. The success of this process depends more on the selection of organic and stripping phases. In this review, the use of liquid membrane technology in treating/recovering copper and silver from industrial e-waste leached solutions was highlighted. It also assembles critical information on the organic phase (carrier and diluent) and stripping phase in liquid membrane formulation for selective copper and silver. In addition, the utilization of green diluent, ionic liquids, and synergist carrier was also included since it gained prominence attention latterly. The future prospects and challenges of this technology were also discussed to ensure the industrialization of technology. Herein, a potential process flowchart for the valorization of e-waste is also proposed.

On-Line Separation and Determination of Trivalent and Hexavalent Chromium with a New Liquid Membrane Annular Contactor Coupled to Inductively Coupled Plasma Optical Emission Spectrometry

We describe a new on-line sensitive and selective procedure for the determination of trivalent and hexavalent chromium in liquid samples by a tailor-made contactor (TMC), specifically a liquid membrane annular TMC, coupled with inductively coupled plasma with optical detection. The TMC was designed and developed to integrate the extraction and stripping phases of the analyte in one module to minimize the membrane solvent’s consumption and maximize the speed of transport through the liquid membrane. Moreover, the particular geometry studied, which consists of two coaxial hollow fibers, allows the TMC to be used for both separating and preconcentrating purposes. Both (−)-N-dodecyl-N-methylephedrinium bromide (30 mM) in dichloroethane and HNO3 (0.75 M) were used as the liquid membrane and receiving solution, respectively. The proposed method’s performance was evaluated in terms of the hexavalent chromium extraction efficiency and the coefficient of variation percentages; these were higher than 85% and less than 5%, respectively. In addition, the proposed procedure was applied to two real samples: a tap water sample and an eluate from solid urban waste. In both cases, the analytical performances were good and comparable to those obtained using synthetic standard solutions.

Recent advances in the removal of pharmaceuticals and endocrine-disrupting compounds in the aquatic system: A case of polymer inclusion membranes

The presence of pharmaceuticals and endocrine-disrupting compounds in aquatic systems is a matter of great concern. The occurrence, fate, and potential toxicity of these compounds have triggered the interest of the scientific community. As a result of their high solubility and low volatility, they are common in aquatic systems, and wastewater treatment plants (WWTP) are the main reservoir for these contaminants. Conventional WWTPs have demonstrated an inability to remove these contaminants completely; hence, different advanced treatment processes have been explored to compensate for the lapses of the conventional system. The outcome of this study revealed the significant improvements made using advanced treatment processes to diminish the number of contaminants; however, some contaminants have proven to be refractory. Thus, there is a need to modify various advanced treatment processes or employ additional treatment processes. Polymer inclusion membranes (PIMs) are a liquid membrane technology that is highly efficient at removing contaminants from water. They have been widely studied for the removal of heavy metals and nutrients from aquatic systems; however, only a few studies have investigated the use of PIMs to remove pharmaceutically active compounds from aquatic systems. This research aims to raise awareness on the application of PIMs as a promising water treatment technology which has a great potential for the remediation of pharmaceuticals and endocrine disruptors in the aquatic system, due to its versatility, ease/low cost of preparation and high contaminant selectivity.

A Critical Study of the Effect of Polymeric Fibers on the Performance of Supported Liquid Membranes in Sample Microextraction for Metals Analysis

Popularity of hollow fiber-supported liquid membranes (HF-SLM) for liquid-phase microextraction (HF-LPME) has increased in the last decades. In particular, HF-SLM are applied for sample treatment in the determination and speciation of metals. Up to the date, optimization of preconcentration systems has been focused on chemical conditions. However, criteria about fiber selection are not reflected in published works. HFs differ in pore size, porosity, wall thickness, etc., which can affect efficiency and/or selectivity of chemical systems in extraction of metals. In this work, Ag+ transport using tri-isobutylphosphine sulfide (TIBPS) has been used as a model to evaluate differences in metal transport due to the properties of three different fibers. Accurel PP 50/280 fibers, with a higher effective surface and smaller wall thickness, showed the highest efficiency for metal transport. Accurel PP Q3/2 exhibited intermediate efficiency but easier handling and, finally, Accurel PP S6/2 fibers, with a higher wall thickness, offered poorer efficiency but the highest stability and capability for metal speciation. Summarizing, selection of the polymeric support of HF-SLM is a key factor in their applicability of LPME for metals in natural waters.

Determination of Cadmium (II) in Aqueous Solutions by In Situ MID-FTIR-PLS Analysis Using a Polymer Inclusion Membrane-Based Sensor: First Considerations

Environmental monitoring is one of the most dynamically developing branches of chemical analysis. In this area, the use of multidimensional techniques and methods is encouraged to allow reliable determinations of metal ions with portable equipment for in-field applications. In this regard, this study presents, for the first time, the capabilities of a polymer inclusion membrane (PIM) sensor to perform cadmium (II) determination in aqueous solutions by in situ visible (VIS) and Mid- Fourier transform infrared spectroscopy (MID-FTIR) analyses of the polymeric films, using a partial least squares (PLS) chemometric approach. The influence of pH and metal content on cadmium (II) extraction, the characterization of its extraction in terms of the adsorption isotherm, enrichment factor and extraction equilibrium were studied. The PLS chemometric algorithm was applied to the spectral data to establish the relationship between cadmium (II) content in the membrane and the absorption spectra. Furthermore, the developed MID-FTIR method was validated through the determination of the figures of merit (accuracy, linearity, sensitivity, analytical sensitivity, minimum discernible concentration difference, mean selectivity, and limits of detection and quantitation). Results showed reliable calibration curves denoting systems' potentiality. Comparable results were obtained in the analysis of real samples (tap, bottle, and pier water) between the new MID-FTIR-PLS PIM based-sensor and F-AAS.

Selective ionic liquid solvent bar micro-extraction for estimation of ultra-trace silver fractions in marine waters

Ag can be found in the ocean at the ultra-trace level, mainly as AgCl_n^(n-1)- and complexed by dissolved organic matter (Ag-DOM). However, methods for studying Ag speciation in marine waters are limited by the lack of extractants capable to separate organic and inorganic silver species in natural conditions of seawater samples. In this work, a two-phase solvent bar micro-extraction method using the ionic liquid trihexyltetradecylphosphonium chloride (Cyphos® 101) was applied for selective micro-extraction of AgCl_n^(n-1)- from organic silver in marine waters, working at seawater pH,. The application to real samples was performed under the following conditions: 2.5% Cyphos® 101 in kerosene solution with 10% dodecan-1-ol inside the fiber, and 30 min of sample extraction at a stirring rate of 800 rpm. The proposed SBME was successfully used for estimation of Ag fractions in waters from the Bay of Cádiz (South-west Spain) showing its applicability for a simple, fast and environmentally friendly speciation of silver in marine water samples. The method presented a linear response up to 500 ng L^-1 and a detection limit of 0.4 ng L^-1, using GF-AAS for instrumental determination.

Design of a Hollow Fiber Supported Liquid Membrane System for Zn Speciation in Natural Waters

A supported liquid membrane-hollow fiber system (HFSLM) has been developed to determine zinc speciation in aquatic environments. The liquid membrane consisted of an organic solution of bis-(2-ethylhexyl)phosphoric acid (D2EHPA) impregnated in the microporous of a polypropylene hollow fiber. The membrane contacted both the donor solution, that contained the metal and the stripping solution, placed in the lumen of the hollow fiber, where the metal was preconcentrated. Different parameters affecting the Zn²⁺ transport efficiency have been evaluated such as the composition of both the donor and stripping solutions as well as the membrane phase. Extraction and transport efficiencies of free Zn(II) higher than 90% were obtained with a liquid membrane consisting of a 0.1 M D2EHPA solution in dodecane and a 0.1 M HNO₃ solution as the stripping phase. The developed HFSLM was used to study the effect of different ligands (EDTA and citric acid) in the donor phase of Zn(II) transport and to investigate the selectivity of the membrane towards Zn when other metals were also present. Finally, the HFSLM system was successfully applied to estimate the free Zn(II) concentrations in three water samples from a mining area. Moreover, the HFSLM system facilitates the analytical determination of trace Zn(II) levels allowing the achievement of enrichment factors of around 700 in the stripping phase.

Applicability of a Supported Liquid Membrane in the Enrichment and Determination of Cadmium from Complex Aqueous Samples

A supported liquid membrane is developed for the separation of Cd from either high in salinity or acidity aqueous media. The membrane consisted of a durapore (polyvinylidene difluoride) polymeric support impregnated with a 0.5 M Aliquat 336 solution in decaline. The effect of carrier concentration, organic solvent and feed and receiving solutions on the metal permeability is studied. This system allows the effective transport of trace levels of Cd through the formation of CdCl₄²⁻, which is the predominant species responsible for the extraction process, in both NaCl and HCl solutions. The supported liquid membrane system in a hollow fibre configuration allows the enrichment and separation of trace levels of Cd from spiked seawater samples, facilitating the analytical determination of this toxic metal.

Liquid Membranes as a Tool for Chemical Speciation of Metals in Natural Waters: Organic and Inorganic Complexes of Nickel

The different species of nickel present in natural waters exhibit different transport behaviour through bulk liquid membranes (BLMs). This fact has been used to design and optimise a separation/pre-concentration system applicable to separate labile and non-labile nickel fractions. A hydrazone derivative—1,2-cyclohexanedione bis-benzoyl-hydrazone (1,2-CHBBH) dissolved in toluene/dimethyl formamide (2% DMF)—was used as a chemical carrier of nickel species, from an aqueous source solution (sample) to a receiving acidic solution. Both chemical and hydrodynamic conditions controlling the transport system were studied and optimised. Under optimum conditions, variations in the transport of nickel ions as a function of organic (humic acids) and inorganic (chloride ions) ligands were studied. Relationships between the permeability coefficient (P) or recovery efficiency (%R) and the concentrations of ligands and nickel species were analysed using Winhumic V software. A negative correlation between P and the concentration of organic nickel complexes was found, suggesting that only labile nickel species are transported through the liquid membrane, with non-labile complexes remaining in the water sample; allowing for their separation and subsequent quantification in natural waters.

Polymer inclusion membranes (PIMs) in chemical analysis - A review

This review highlights the increasing interest in polymer inclusion membranes (PIMs) in analytical chemistry as they are adapted to new and novel applications. PIMs are polymer-based liquid membranes and were first introduced 50 years ago as the sensing membranes in ion-selective electrodes and optodes. More recently however, PIMs have been used for other applications in analytical chemistry such as for sample separation, sample pre-concentration, electro-driven extraction, and passive sampling, and have also been incorporated into on-line and automated analysis systems. The present review provides a general overview of the analytical chemistry applications of PIMs reported in the literature to date and illustrates their versatility for solving challenging chemical analysis problems.

Nickel (II) Preconcentration and Speciation Analysis During Transport from Aqueous Solutions Using a Hollow-fiber Permeation Liquid Membrane (HFPLM) Device

Nickel (II) preconcentration and speciation analysis using a hollow fiber supported liquid membrane (HFSLM) device was studied. A counterflow of protons coupled to complexation with formate provided the driving force of the process, while Kelex 100 was employed as carrier. The influence of variables related to module configuration (acceptor pH and carrier concentration) and to the sample properties (donor pH) on the preconcentration factor, E, was simultaneously studied and optimized using a 3 factor Doehlert matrix response surface methodology. The effect of metal concentration was studied as well. Preconcentration factors as high as 4240 were observed depending on the values of the different variables. The effects of the presence of inorganic anions (NO₂⁻, SO₄²⁻, Cl⁻, NO₃⁻, CO₃²⁻, CN⁻) and dissolved organic matter (DOM) in the form of humic acids were additionally considered in order to carry out a speciation analysis study. Nickel preconcentration was observed to be independent of both effects, except when cyanide was present in the donor phase. A characterization of the transport regime was performed through the analysis of the dependence of E on the temperature. E increases with the increase in temperature according to the equation E(K) = −8617.3 + 30.5T with an activation energy of 56.7 kJ mol⁻¹ suggesting a kinetic-controlled regime. Sample depletion ranged from 12 to 1.2% depending on the volume of the donor phase (100 to 1000 mL, respectively).

Synthesis and adsorption performance of lead ion-imprinted micro-beads with combination of two functional monomers

A novel ion-imprinted polymer, lead ion-imprinted micro-beads with combination of two functional monomers, was synthesized using the W/O/W polymerization method. Two functional monomers, 1,12-dodecanediol-O,O'-diphenyl-phosphonic acid (DDDPA) and 4-vinylpyridine, were used to form a suitable construction with micro-pores fitting the template and recognition sites. The effects of adsorbent dosage, solution pH and the competitive ions on the adsorption and separation efficiency of lead ions were investigated. The lead ion-imprinted micro-beads were efficient for lead ions removal from aqueous solution in a broad pH range (4-9), when the adsorbent dosage was above 0.1 g/L. The adsorption process obeyed the pseudo second-order kinetics model and it only took half an hour to reach the equilibrium. The adsorption isotherm of lead ion was described by the Langmuir model (R2 > 0.99) with a maximum adsorption capacity of 116.9 mg/g. In the presence of competitive ions Co2+ and Cd2+, the lead ion-imprinted micro-beads showed a high selectivity for lead ions. The selectivity coefficient of Pb2+/Cd2+ and Pb2+/Co2+ are 99.3 and 114.7, respectively.